Apparatus, a Handheld Electronic Device, and a Method for Carrying Out Raman Spectroscopy

ABSTRACT

An apparatus, a handheld electronic device and a method for carrying out Raman Spectroscopy are disclosed. In an embodiment an apparatus includes at least one optoelectronic laser configured to provide excitation radiation to a sample, the excitation radiation being generated by an electric current flowing through the at least one optoelectronic laser during operation of the apparatus and a transistor configured to modulate the electric current flowing through the at least one optoelectronic laser, to thereby switch on and off generation of the excitation radiation.

TECHNICAL FIELD

The present disclosure relates to an apparatus for carrying out Ramanspectroscopy on a sample. The present disclosure relates to a handheldelectronic device and a method for carrying out Raman spectroscopy on asample.

BACKGROUND

The chemistry of samples, such as molecules, can be probed by exposing asample to laser light and by collecting the inelastically backscatteredlight. Light at a wavelength of the laser light in the backscatteredlight, also referred to as Rayleigh scattering, can be filtered outusing, for example, a high pass filter. The remaining red shifted light,also called Raman scattered light, can be imaged onto a detector. Thismethod of probing matter is a common way to obtain a unique Ramanspectrum with greater accuracy than broadband spectroscopy and it can beused to reliably identify the chemical makeup and structure of thematter in question. When examining, for example, biological media, aproblem can be the occurrence of fluorescence light which can be severalorders of magnitude greater than the Raman signal, and the fluorescencelight can obfuscate the identifying information.

A repeatable, portable and affordable apparatus and method is sought tocarry out Raman spectroscopy on a sample, for example to identifypesticides on food, drugs in urine and contamination in liquid milk.

SUMMARY

Embodiments of the invention seek to provide an apparatus for carryingout Raman spectroscopy, such as time-gated Raman spectroscopy, on asample. The apparatus comprises at least one optoelectronic laser forproviding excitation radiation to the sample, the excitation radiationbeing generated by an electric current which flows through the at leastone optoelectronic laser during operation of the apparatus, and atransistor, such as a GaN FET, for modulating the electric currentflowing through the at least one optoelectronic laser, to thereby switchon and off the generation of the excitation radiation.

The at least one optoelectronic laser can be one or more optoelectroniclasers, and the electric currents that flow through the optoelectroniclasers can be different from each other. However, the transistor can beemployed to control each of the electric currents simultaneously. Theelectric current through an optoelectronic laser causes the generationof coherent laser light. A GaN FET (FET=field effect transistor) allowsrapid control of the electric current, and thus, it can be employed toswitch on and off the generation of excitation radiation. Time gatedRaman spectroscopy can therefore be carried out.

For example, the transistor can modulate the electric current such as toswitch intermittently an optoelectronic laser between on operationalmode and a non-operational mode. The laser can emit pulses of excitationradiation in the operational mode. The electric current is then at alevel at which the pulses of excitation radiation can be generated. Inthe non-operational mode, the electric current is at a level where lightemission does not occur.

Raman measurements on a sample will lead to fluorescence when trying tocollect a Raman signal. The concept of time-gated Raman scattering isrelated to the aspect of collecting Raman scattering prior tofluorescence. For example, laser pulses with a time duration in thepico-second range can be used to stimulate the immediate Ramanscattering prior to the fluorescing portion saturating a detector, whichis used to detect the Raman light. Raman scattering of a sample isproportional to 1/λ{circumflex over ( )}4, wherein λ denotes thewavelength of the excitation radiation. It can for example be possibleto use direct transition 520 nm picosecond laser light to stimulateintense Raman scattering without damaging a sample.

In some embodiments, the at least one optoelectronic laser is configuredto provide single mode operation which is wavelength stabilized, and/orto maintain a wavelength in a robust way and for a long time, and/or toprovide excitation radiation with a long coherence length.

In some embodiments, the at least one optoelectronic laser comprises asemiconductor based lasing device, in particular a laser diode. In someembodiments, the laser diode emits green light, for example at awavelength of 520 nm.

In some embodiments, the semiconductor based lasing device can have aDBR (=Distributed Bragg Reflector) or DFB (=Distributed feedback) orVCSEL (=vertical-cavity surface-emitting laser) architecture. Thus, forexample, the optoelectronic laser can be a DBR or DFB laser diode or aVCSEL.

A distributed Bragg reflector is a periodic structure, which is formedof alternating dielectric layers having different indices of refraction.A DBR might be used to achieve nearly total reflection within a range offrequencies, wherein the range of frequencies includes the frequenciesof the excitation radiation of the laser. The DBR can be formed by useof dielectric layers that are included in the layer structure of thelaser.

A distributed feedback laser diode can be a type of laser diode, quantumcascade laser or optical fiber laser where the active region of thedevice contains a periodically structured element or diffractiongrating.

A VCSEL is a type of semiconductor laser diode that emits laser light ina direction, which is perpendicular to the top surface of the laserdiode.

In some embodiments, the at least one optoelectronic laser is a DFB orDBR laser diode.

In some embodiments, the at least one optoelectronic laser comprises alaser diode and at least one of an external cavity and a wavelengthmultiplexer.

In some embodiments, the at least one optoelectronic laser can be two,three or more lasers. For example, each laser can be a laser diode thatprovides laser light at a defined wavelength. The light from the laserdiodes can be coupled, for example by use of a combiner, into a singlefiber or into a single, preferably collimated, beam. For example, usingthree laser diodes, one emitting red light, one emitting green light,and one emitting blue light, a laser beam including the red, green andblue light can be obtained. Thus, an RGB laser beam could be obtained.

In some embodiments, the transistor is a Gallium Nitride field effecttransistor (GaN FET). The GaN FET can be configured as a high-power GaNFET. The GaN FET can be configured to allow picosecond rise times,thereby enabling the optoelectronic laser to generate pulses with a timeduration in the pico-second range.

In some embodiments, the transistor is embedded in a substrate, whereinan optoelectronic laser is arranged on the substrate. The optoelectroniclaser and the transistor can be accommodated in a single package. As thetransistor can be placed directly underneath the optoelectronic laser,basically none or only very short wiring is required to connectelectrically the transistor to the optoelectronic laser. Thus, thetransistor can be electrically coupled to the optoelectronic laser atleast in substance without using bond wires. This allows short switchingtimes of a voltage provided by use of the transistor to theoptoelectronic laser. For example, a change in voltage (V) over time(t), dV/dt, can be larger than 100 V/s. For an optoelectronic laser withapproximately 8V forward bias, this can for example result in a turn onand off time of 160 ps.

In some embodiments, the at least one optoelectronic laser andoptionally the transistor can be arranged in a package. A connecting padcan be placed under the at least one optoelectronic laser, and thetransistor can be placed on or beyond the connecting pad. The at leastone optoelectronic laser in the package is preferably a DFB or DBR laserdiode.

In some embodiments, the GaN FET has an electric contact and anoptoelectronic laser has an electric contact, and the electric contactof the transistor is directly coupled electrically to the electriccontact of the optoelectronic laser. Basically no bond wire is used toconnect the electric contacts of the transistor and the optoelectroniclaser.

The transistor can be an FET transistor which has a drain electrode. Theoptoelectronic laser can be a laser diode which has a cathode and ananode. In some embodiments, the drain of the FET transistor can bedirectly coupled to the cathode of the laser diode. This allows forshort switching times.

In some embodiments, a driver is configured to operate the transistorsuch as to cause the optoelectronic laser to cause the generation ofpulsed excitation radiation. The driver can provide a control signal tothe transistor. The control signal can also be called frame sync signal.

For example, if the transistor is a FET transistor, the driver canprovide the control signal to the gate of the transistor. The cathode ofthe laser diode can be connected to the drain of the FET transistor. Theapplication of a voltage to the gate by use of the control signal allowsmodulating the electric current through the laser diode. Thereby, thelaser diode can be rapidly switched between an on state and an offstate. The control signal can for example be a square-wave signal.

In some embodiments, the at least one optoelectronic laser can beconfigured to generate pulsed excitation radiation, with pulses having atime duration of less than 100 picosecond. The pulse duration can bemeasured at FWHM (=full width have maximum). The pulse duration cantherefore correspond to the full width at half of the maximum of thetime signal of a pulse.

In some embodiments, the at least one optoelectronic laser can beoperated to generate pulses of excitation radiation, wherein each pulsehas for example a time duration of less than 500 ps or less than 500 fs.

In some embodiments, the apparatus comprises a temperature sensorconfigured to monitor a temperature of an optoelectronic laser. A changein temperature can cause a wavelength shift in the emitted excitationradiation from the optoelectronic laser. Such a wavelength shift canthus be accounted for by monitoring the temperature.

In some embodiments, the apparatus comprises a Bragg grating.

The Bragg grating can be helpful in producing laser light with a longcoherence length. The Bragg grating can be integrated into a package,which further includes the optoelectronic light source and thetransistor. Such a package may have, but does not require a non-hermeticfacet coating, which is preferably used in conjunction with DFB or DBRlaser diodes.

In some embodiments, the apparatus comprises a spectrometer foranalyzing Raman light scattered from the sample in response to exposingthe sample to the excitation radiation, the Raman light comprising oneor more spectral components, and wherein the spectrometer comprises adiffraction element configured to split the Raman light into itsspectral components.

Thus, the diffraction element can divide the Raman light into itsspectral components and thereby spread the Raman light into an opticalspectrum of spatially separated wavelength components.

The spectrometer can further comprise a focusing lens system fordirecting at least a portion of the spectrum to a detector, such as aone- or two-dimensional array detector.

The spectrometer can comprise an entrance slit. The slit can help totighten the window of observation for Raman scattering prior tofluorescence, thereby eliminating fluorescence, which will preventcollection of the Raman signal.

In some embodiments, the diffraction element comprises at least one ofthe following: a diffraction grating, a photonic crystal, and aplasmonic Fabry Perot filter.

In some embodiments, the apparatus includes a scanning mirror in a lightpath of the Raman scattered light, in particular between a spectrometerand a detector, wherein the transistor is operated based on a controlsignal, and wherein the scanning mirror is also operated based on thecontrol signal.

Embodiments of the invention relate to a handheld electronic devicewhich comprises a housing, and an apparatus with at least oneoptoelectronic laser for providing excitation radiation to the sample,the excitation radiation being generated by an electric current whichflows through the at least one optoelectronic laser during operation ofthe apparatus, and the apparatus further comprising a transistor formodulating the electric current flowing through the at least oneoptoelectronic laser, to thereby switch on and off the generation of theexcitation radiation and the apparatus being arranged in the housing ofthe handheld electronic device.

In some embodiments, the handheld electronic device is a smartphone or atablet.

Embodiments of the invention also relate to a method of carrying outRaman spectroscopy on a sample, wherein the method comprises providingan apparatus in accordance with at least some of the embodiments asdescribed herein, and operating the transistor, for example a GaN FET,such as to cause the optoelectronic laser to generate pulses ofexcitation radiation.

A feature mentioned in conjunction with an embodiment can also bepresent in another embodiment, even if not explicitly mentioned inconjunction with this embodiment.

The sample is not a part of the claimed apparatus, handheld electronicdevice or method. Rather, the sample is the piece of matter or a volumeof gas or liquid on which Raman spectroscopy is carried out.

The electric current flows through the optoelectronic laser duringoperation of the laser and thus during the intended use of the apparatusor handheld electronic device.

In some embodiments, a handheld electronic device can comprise anapparatus for carrying out Raman spectroscopy on a sample using timegated Raman spectroscopy via direct modulation of a laser diode and MEMSmirrors plus slits to image Raman scattering prior to fluorescence aswell as various instantiations using Bragg gratings (single wavelengthlaser) versus multiwavelengths (surface relief gratings). MEMS mirrorsplus a double slits and various types of detectors (filter array,electrostatically charged deep well large pixels, Chromation device,etc.) can all provide various ways to detect separated Raman scattering.The use of double slits with a MEMS mirror prevents saturation of theRaman signal by the following fluorescence.

In some embodiments, an apparatus for carrying out Raman spectroscopycomprises a GaN FET, and a directly modulated (by the GaN FET), visibleDFB or DBR laser which is used to generate laser pulses fast enough (forexample <200 ps) to capture Raman scattering prior to fluorescence.Tandem slits and/or MEMS mirrors can be used to image while a lasermodulation signal is used to as a frame sync. The laser modulationsignal can be provided by a driver which drives the transistor based onthe laser modulation signal. The use of small laser diodes, MEMSmirrors, and linear arrays as detectors can mean that the apparatus canfit into a handheld device, such as a cell phone, smart phone, tablet,etc.

BRIEF DESCRIPTION OF THE DRAWINGS

One or more examples will hereinafter be described in conjunction withthe following drawing figures, where like numerals denote like elements.

FIG. 1 shows a block diagram of an exemplary embodiment of an apparatus;

FIG. 2 shows schematically an exemplary embodiment of a handheldelectronic device;

FIG. 3 illustrates schematically a functional approach for carrying outtime-gated Raman spectroscopy;

FIG. 4 illustrates schematically a further functional approach forcarrying out time-gated Raman spectroscopy;

FIG. 5 shows schematically a further exemplary embodiment of anapparatus;

FIG. 6 shows schematically a further exemplary embodiment of anapparatus;

FIG. 7 shows schematically a further exemplary embodiment of anapparatus; and

FIG. 8 shows schematically yet a further exemplary embodiment of anapparatus.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The apparatus 101 as shown in FIG. 1 can be used for carrying out Ramanspectroscopy, such as time-gated Raman spectroscopy, on a sample 103,which is not part of the apparatus 101. The apparatus 101 comprises anoptoelectronic laser 105 for providing excitation radiation to thesample 103. The sample 103 can be arranged, for example by a user of theapparatus, such that it can be exposed to the excitation radiation,which usually consists of or comprises laser light.

The apparatus 101 further comprises a transistor 107, for example aGallium Nitride field effect transistor, for modulating an electriccurrent, which flows during operation of the apparatus 101 through theoptoelectronic laser 105 and which causes the generation of theexcitation radiation.

At least some embodiments of the apparatus 101 can be incorporated intoa handheld electronic device, such as a cell phone, a smartphone or atablet computer. For example, the handheld electronic device 201 of FIG.2 comprises such an apparatus having an optoelectronic laser 203, forexample a DFB or DBR laser diode, for providing excitation radiation 207to sample 205, which is arranged outside a housing 209 of the handheldelectronic device 201.

The excitation radiation 207 can have an average power of more than womW. The excitation radiation can comprise green laser light, and theexcitation radiation can include one or more wavelengths. For example,two wavelengths, one in the visible and one in the infrared, can help toobtain a better confirmation of the Raman signal.

The apparatus 201 also comprises a transistor 211, such as a GaN FET,for modulating an electric current, which can flow through theoptoelectronic laser 203 to cause the generation of the excitationradiation 207.

The apparatus 201 also includes an objective 213, for example in form ofa focusing lens system which can comprise a plano convex lens. Theobjective 213 can focus the excitation radiation 207 to a spot 215outside the housing 209. The sample 207 is placed such that the spot 215is located on the surface of the sample 205. The objective 213 alsoserves to collect light scattered from the sample 205. The scatteredlight includes Raman scattered light with wavelengths that are differentfrom the wavelengths of the excitation radiation 207.

A high pass filter 217 is configured to reflect the excitation radiation207 from the optoelectronic laser 203 and to guide the excitationradiation 207 to the objective 213. The high pass filter 217 isfurthermore transparent for light with wavelengths, which are longerthan the wavelengths of the excitation radiation 207. Thus, the redshifted portion of the Raman scattered light can pass the high passfilter 217 and it can be focused through a slit 219 of a spectrometer221.

The spectrometer 221 comprises a diffraction element 223, such as adiffraction grating, a photonic crystal, or a plasmonic Fabry Perotfilter, which spatially splits the Raman light into its spectralcomponents. A focusing lens system (not shown) images the spectralcomponents on an array detector, such as a CCD array detector(CCD=charged coupled device).

The diagram 15 as shown in FIG. 3 illustrates a time-gated Ramanspectroscopy process. The diagram 15 is also related to the setup ofFIG. 5, which will be described further below in more detail.

As illustrated in 301 of FIG. 3, an optoelectronic laser is operatedsuch as to provide laser pulses. The laser can be a low power (forexample with an average power of 100 mW) DFB or DBR laser diode. A laserdiode 9 is shown in FIG. 5.

Alternatively, a VCSEL and a green laser, such as a direct transitiongreen laser, could be used to provide laser light. The VCSEL can forexample be configured to emit light in the infrared.

A control signal (frame sync signal) 11 is generated in 303, which isused for controlling the operation of the laser 9. The signal 11 canalso trigger the flashing of a detector array, for example, a lineararray, from existing charges according to 305.

Regarding the generated laser pulse, it is reflected off the filter 2(see FIG. 5) according to 307. In 309, the pulse travels throughobjective 1 and hits sample 215 (see also FIG. 5). Light which includesRaman light is back scattered and collected by the objective 1 accordingto 311 of FIG. 3. The red-shifted Raman light passes the high passfilter 2, and lens 3 focuses the light through slit 4 into thespectrometer according to 313 of FIG. 3.

The Raman light further passes through collimation and aberrationcorrection optics 5 and diffracting element 6 which spatially splits theRaman light into its spectral lines. At least some of the spectral linesin the Raman light are imaged by use of imaging lens 7 on the detector8. A shutter 14 is placed in front of the detector 8 and the shutter 14is operated based on the frame sync signal 11 by use of which the laser9 is operated. As indicated in 315, the frame sync signal 11 allows thedetector to collect the spectral lines of the Raman light by causing theopening of the shutter 14.

Fluorescence is generated by the sample according to 317 with a timedelay with regard to the Raman light. Fluorescence light can arrive atthe detector 8 according to 319, but data about the spectral lines inthe Raman signal have already been collected due to the use of the framesync signal as shown in 315 which has in the meantime closed the shutter14. Thus, the detector 8 will not collect fluorescence light.

The data collected in 315 will be further processed in 312, for exampleby use of an artificial intelligence (AI) system or the like, in orderto identify the spectral lines and/or the sample. A result is output in323.

The diagram 25 as shown in FIG. 4 differs from the diagram 15 in FIG. 3by block 401. Instead of using a shutter 14 (see FIG. 5), double slits46 and 48 and a scanning mirror 47, for example a MEMS scanning mirror(MEMS=Micro-Electro-Mechanical System) are used, as illustrated in FIG.6. The use of a MEMS scanning mirror 47 allows reduction of exposuretime and prevents saturation of the linear array 8, trimming out theundesirable fluorescence in a different manner than shutter 14.

In some embodiments, this can be similar to tandem slit scanningmicroscopy. A tandem scanning slit microscope is for example describedin the scientific publication by Stephen C. Baer “Tandem Scanning SlitMicroscope”, Proc. SPIE 1139, Optical Storage and Scanning Technology,(28 Sep. 1989); https://doi.org/10.1117/12.961780.

For example, in order to confine illumination to just the plane offocus, a tandem scanning mirror can be used similar to anepi-illumination tandem scanning pinhole microscope using slits instead.Epi-illumination is an operational mode used in microscopy in whichillumination and detection occurs from the same side of the sample. Themirror image of one field aperture is coincident with the other, wherean opaque mirror is used at the edge of the plane defined by the viewingslit and the center of the objective aperture. The mirror can thenreflect light from the illuminated slit onto just one semicircle of theobjective aperture. The remaining semicircle can be used for projectinglight from the specimen to the viewing slit. Scanning can beaccomplished by reciprocally rotating the two slits and the mirror. MEMScan be used to achieve rotating movements.

As further shown in diagram 35 of FIG. 5, the operation ofoptoelectronic laser 9 is controlled via GaN FET 10. The laser 9comprises an anode A and a cathode C. The anode A is connected to avoltage supply provided by a voltage source (not shown). The cathode Cis electrically connected to the drain D of transistor 10. The source Sof transistor 10 is connected to ground gnd. The control signal (framesync signal) 11 is applied to the gate of transistor 10. The controlsignal 10 can for example be a square-wave signal, and it can beconfigured to rapidly switch the electric current that drives the laser9 between a level at which lasing occurs and a level at which the laser9 is not emitting light.

The control signal 10 is provided to the shutter 14 to open and closethe shutter 14 in dependence on the control signal 14. In the setup 45of FIG. 6, the control signal 10 can be used to control the operation ofthe scanning mirror 47.

The laser 9 is turned on and off using the GaN FET 10, which can forexample switch at dV/dt>100V/s. For example, the laser 9 can have anapproximate 8V forward bias, a turn on and off time of 160 ps is thenpossible. As the laser 9 can be a low power laser, it will not require ahigh voltage rail. The GaN FET 10 is well suited for these types of fastswitching applications.

The generated pulses of the excitation radiation provided by the laserdiode 9 is collimated using a lens 12, which can produce a Gaussian beamwhich is desirable for accurate Raman scattering analysis. The pulses ofthe excitation radiation are then condensed via objective 1, alsoreferred to as probe optics, for example by using a common low f-numberoptics.

The pulses of laser light can be focused down to a spot size ofapproximately 20 microns to stimulate Raman scattering on the sample215.

The backscattered light is mostly rejected at high pass filter 2, whichcan be a dichroic mirror, except the red-shifted component of the Ramanscattered light. Thus, only the Stokes shifted light of the Raman lightis further processed. The high pass filter 2 can start at the laserwavelength of the pulses as provided by laser 9, for examplecorresponding to a wavelength of 520 nm, 785 nm, 850 nm, or 940 nm.

Condensing lens 3 focuses the pulses of Raman light through slit 4 whichdetermines the resolution of the system and optical throughput. Forexample, a 10-50 micron slit 4 is used to filter the signal. The pulsesof Raman light pass through collimation and aberration correction optics5, such as anachromat. The expanded and somewhat collimated pulses passthrough diffracting element 6 which can be a 2D photonic crystal or avolume Bragg grating, and it acts as a wavelength separator.

Imaging lens 7 directs the first order of the spatially separated linesof the Raman light towards detector 8 while avoiding the zero order. Theshutter 14 is used to prevent fluorescence light from saturating thedetector 8 and the shutter 14 is operated based on the frame sync signal11.

The now wavelength separated Raman light is imaged on detector 8, forexample a linear array 8 such as a SiPM, SPAD, InGaAS detector, or cutfiltered silicon with bias voltage applied.

The frame sync 11 can also be used to clear excess charges prior toRaman scattering being imaged on the detector 8.

The linear array 8 can be a deep well, large pixel (for example 8 um×8um) linear array, and it can display an extremely tight form factor (8mm×1 mm).

A temperature sensor or TEC 13 can be used to monitor the laser diodetemperature to account for wavelength shift of laser diode 9.

As shown in FIG. 7, the setup 55 provides multiple wavelengths ofexcitation radiation to sample 215. This can be realized by use of threelasers 9, 58, and 59, each of which provides laser pulses at aparticular wavelength. Each laser 9, 58, and 59 is a laser diode and thecathode C of each laser diode is connected to the drain D of transistor10.

The control signal 11 is applied to gate G of transistor 10 to controlthe electric current through the laser diodes 9, 58, and 59 and, thus,to switch the lasers 9, 58, and 59 on and off. The control signal 11 isalso used to control the operation of the shutter 14.

A blazed diffraction grating 56 is further used to diffract anywavelength. For example, consider a 520 nm laser 9, a 785 nm laser 58,and an infrared laser 59 providing pulses at 1064 nm. The control signal11 is again used along with a shutter 14 and linear array 8.

As an alternative to the diffraction grating 56, the Raman scatteredlight from the sample 215 under investigation can be split into itsspectral lines by means of a prism or optical grating to fall onto alinear detector grid. The respective spectrum can be derived from thelight intensity on each of the linearly aligned detector elements ofdetector 8.

In some alternative embodiments, the Raman light is directed to a sensorarray, where each sensitive element or pixel is using a unique filterthat only allows a specified narrow waveband to reach the sensorelement. In this way, a diffraction element is not required. The numberof pixels and the bandwidth of each corresponding filter in front ofeach pixel determine the spatial resolution of the detected spectrum.

The setup 65 as shown in FIG. 8 includes double slits 46 and 48 as wellas scanner 47 instead of the shutter 14 as used in setup 55 of FIG. 7.The control signal 11 is used to control operation of the scanner 47,which can be a scanning mirror or a MEMS scanning mirror. A multiplexingwaveguide can also be utilized. The waveguide can be used for compactlycombining multiple wavelengths such as those used, for example, incommunication servers.

The foregoing description, for purpose of explanation, has beendescribed with reference to specific embodiments. However, theillustrative discussions above are not intended to be exhaustive or tolimit the invention to the precise forms disclosed. Many modificationsand variations are possible in view of the above teachings. Theembodiments were chosen and described in order to best explain theprinciples of the techniques and their practical applications. Othersskilled in the art are thereby enabled to best utilize the techniquesand various embodiments with various modifications as are suited to theparticular use contemplated.

What is claimed is:
 1. An apparatus for carrying out Raman spectroscopyon a sample, the apparatus comprising: at least one optoelectronic laserconfigured to provide excitation radiation to the sample, the excitationradiation being generated by an electric current flowing through the atleast one optoelectronic laser during operation of the apparatus; and atransistor configured to modulate the electric current flowing throughthe at least one optoelectronic laser, to thereby switch on and offgeneration of the excitation radiation.
 2. The apparatus of claim 1,wherein the at least one optoelectronic laser is a DFB laser diode orDBR laser diode.
 3. The apparatus of claim 1, wherein the transistorcomprises an electric contact and the optoelectronic laser comprises anelectric contact, and wherein the electric contact of the transistor isdirectly coupled electrically to the electric contact of theoptoelectronic laser.
 4. The apparatus of claim 1, wherein thetransistor is a GaN FET configured to operate the at least oneoptoelectronic laser such as to generate pulsed excitation radiation. 5.The apparatus of claim 1, wherein the at least one optoelectronic laseris configured to generate pulses of excitation light, wherein each pulsehas a time duration of less than 200 ps.
 6. The apparatus of claim 1,further comprising a temperature sensor configured to monitor atemperature of the at least one optoelectronic laser.
 7. The apparatusof claim 1, further comprising a Bragg grating.
 8. The apparatus ofclaim 1, further comprising a spectrometer configured to analyse Ramanlight scattered from the sample in response to exposing the sample tothe excitation radiation, wherein Raman light comprises one or morespectral components, and wherein the spectrometer comprises diffractionelement configured to split the Raman light into its spectralcomponents.
 9. The apparatus of claim 8, wherein the diffraction elementcomprises at least one of the following: a diffraction grating, aphotonic crystal, or a plasmonic Fabry Perot filter.
 10. The apparatusof claim 1, further comprising a driver for the transistor, wherein thedriver is configured to provide a control signal for controllingoperation of the transistor.
 11. The apparatus of claim 10, furthercomprising a shutter between a spectrometer and a detector configured todetect spectral lines in a Raman signal, wherein the spectral lines arespatially split by the spectrometer from the Raman signal, and whereinthe shutter is operated based on the control signal.
 12. The apparatusof claim 10, further comprising a scanning mirror between a spectrometerand a detector for detecting spectral lines in a Raman signal, whereinthe spectral lines are spatially split by the spectrometer from theRaman signal, and wherein the scanning mirror is operated based on thecontrol signal.
 13. A handheld electronic device comprising: a housing;and an apparatus with at least one optoelectronic laser configured toprovide excitation radiation to a sample, the excitation radiation beinggenerated by an electric current flowing through the at least oneoptoelectronic laser during operation of the apparatus, wherein theapparatus further comprises a transistor configured to modulate theelectric current flowing through the at least one optoelectronic laser,to thereby switch on and off generation of the excitation radiation, andwherein the apparatus is arranged in the housing of the handheldelectronic device.
 14. The handheld electronic device of claim 13,wherein the handheld electronic device is a smartphone or a tablet. 15.A method of carrying out Raman spectroscopy on a sample, the methodcomprising: providing, by at least one optoelectronic laser of anapparatus, excitation radiation to the sample, the excitation radiationbeing generated by an electric current flowing through the at least oneoptoelectronic laser during operation of the apparatus, wherein theapparatus further comprises a transistor for modulating the electriccurrent flowing through the at least one optoelectronic laser, tothereby switch on and off generation of the excitation radiation; andoperating the transistor such as to cause the at least oneoptoelectronic laser to generate pulses of excitation radiation.
 16. Anapparatus for carrying out Raman spectroscopy on a sample, the apparatuscomprising: a GaN FET; and at least one DFB or DBR laser, wherein theGaN FET is configured to directly modulate the DFB or DBR laser forgenerating at least one laser pulse which fast enough to capture Ramanscatter prior to fluorescence.
 17. The apparatus of claim 16, furthercomprising tandem slits and/or MEMS mirrors configured to image while alaser modulation signal is used to as a frame sync.